Gio found $16$ apples that had fallen from the apple trees in her yard. There were still $21$ apples in the trees. How many apples were in the trees before the apples fell?
Answer: To find the ${\text{total}}$ number of apples in the tree before they fell, we start with the number of ${\text{Apples on the ground}}$, and add the number of ${\text{Apples left in the tree}}$. $?$ $16$ $21$ Total number of apples Apples on the ground Apples left in the tree ${16} + {21} = {\Box}$ Let's add to find the total number of apples. $$ $$ $$ ${+}$ $$ $$ $$ ${=}$ $$ $$ $$ $$ $$ ${16} + {21} = {37}$ There were ${37}$ apples in the trees before the apples fell to the ground.